1. Field of the Invention
The present invention relates to a display apparatus, such as a liquid crystal display apparatus and an electroluminescence display apparatus, and to a method for manufacturing a substrate for the display apparatus.
2. Description of Related Art
In order to enhance the display quality of a liquid crystal display apparatus, it is important to control the applied voltage to the liquid crystal. In particular, if the gap of the liquid crystal is not uniform in the display area of a liquid crystal display panel, a difference is generated in the phase change of liquid crystal. As the result, brightness unevenness may occur in a displayed image.
For this reason, it is important to equalize the thickness of a film layer, such as a wiring film and an insulating film, in the display area of the liquid crystal display panel. These wiring film, insulating film, etc. are formed over an active matrix substrate where a switching element, such as a TFT (Thin Film Transistor), is formed.
The liquid crystal display panel of the liquid crystal display apparatus includes the active matrix substrate described above and an opposite substrate provided opposite to the active matrix substrate. In the manufacturing process of the liquid crystal display panel of the liquid crystal display apparatus, a resin insulating film, a color filter, a resin black matrix (resin BM), and an overcoat layer are applied to the active matrix substrate, the opposite substrate, etc. Moreover, an organic film, such as resist, used for photolithography process and removed after pattern formation is also applied. When applying these, a spin coat method is used in many cases. In the conventional manufacturing process for a liquid crystal display apparatus where the spin coat method is used, the thickness of an organic film coated by the spin coat method may become uneven. Therefore, there is a problem that spatial coating unevenness occurs in the thickness of the coated organic film. This is because when the size of a wiring pattern or an insulating film pattern which is an underlying material of the organic film is large, the thickness of the organic film is affected by the shape of the pattern. Specifically, since there exists a step (level difference) of the large pattern, solution of the organic film flows along the pattern by centrifugal force at the time of spin coating. Then, the solution of the organic film, flowing along the pattern, flows outside from the corner or the end of the pattern by the centrifugal force. For this reason, after the solvent of the solution of the organic film volatilizes, large linear unevenness extending from the corner or the end of the pattern is generated, in the organic film. As to this problem, a difficulty solution example is disclosed in Japanese Patent Application Laid-open No. 2002-350820. In the liquid crystal display apparatus disclosed in Japanese Patent Application Laid-open No. 2002-350820, the shape of wiring provided on the periphery of the display area of the active matrix substrate, where a TFT element is formed, is as shown in FIG. 7. That is, a large number of small projections 9 are formed on the wiring 8. The arrow in FIG. 7 indicates a substrate center direction 11 used as a rotary shaft at the time of spin coating. Owing to the structure as shown in FIG. 7, when solution of the organic film applied by spin coating flows in the direction opposite to the substrate center direction 11 by centrifugal force, it is possible to prevent flowing along the wiring 8.
However, the flow of the solution of the organic film is prevented by the large number of small projections 9 formed on the wiring 8 serving as an underlying material in the display apparatus described in Japanese Patent Application Laid-open No. 2002-350820. For this reason, there are generated a large number of small linear coating unevennesses 10 where the thickness of the organic film is not uniform. Such coating unevenness 10 is generated starting from the corner of the projection 9, in the opposite side of the substrate center direction 11. Therefore, the problem of causing degradation of the display quality still remains. In order to enhance the display quality, it is necessary to form film layers, accumulated over the opposite substrate in addition to over the active matrix substrate, so that they may not have thickness unevenness. Specifically, it is necessary to form a color filter, a resin BM, an overcoat layer, a pillar-shaped spacer, etc. over the opposite substrate so that they may have no unevenness in thickness. However, because of the shape of other film layer (ex. color filter) serving as the underlying material, the organic film which is applied by spin coating may have coating unevenness.
Furthermore, the generation of the problem mentioned above is not limited to when forming a film layer by spin coating over the substrate for a liquid crystal display apparatus. That is, this problem also occurs when forming a film layer by spin coating in other display apparatus, such as an electroluminescence display apparatus.